Multi-piece baffle plate assembly for a plasma processing system

ABSTRACT

A plasma processing system includes at least one multi-piece baffle plate. The multi-piece baffle plate assembly generally comprises at least one annular shaped ring portion having an opening and an insert portion dimensioned to sit within the opening. The individual pieces can be formed of a ceramic material. The effects caused by thermal gradients in the plate during plasma processing are minimized.

BACKGROUND

In the manufacture of integrated circuits, photolithography techniques are used to form integrated circuit patterns on a substrate, such a silicon wafer. Typically, the substrate is coated with a photoresist, portions of which are exposed to ultraviolet (UV) radiation through a mask to image a desired circuit pattern on the photoresist. The portions of the photoresist left unexposed to the UV radiation are removed by a processing solution, leaving only the exposed portions on the substrate. These remaining exposed portions may be baked during a photostabilization process to enable the photoresist to withstand subsequent processing.

After such processing, in which the integrated circuit components are formed, it is generally necessary to remove the baked photoresist from the wafer. In addition, residue that has been introduced on the substrate surface through processes such as etching must be removed. Typically, the photoresist is “ashed” or “burned” and the ashed or burned photoresist, along with the residue, is “stripped” or “cleaned” from the surface of the substrate.

One manner of removing photoresist and residues is by rapidly heating the photoresist-covered substrate in a vacuum chamber to a preset temperature by infrared radiation, and directing microwave-energized or radio frequency (RF) energized reactive gases (i.e., a plasma) toward the heated substrate surface. In the resulting process, the reactive plasma reacts with the photoresist to ash it for subsequent removal from the wafer.

It is important that the ashing process occur at substantially the same rate across the surface of the wafer. To insure such uniform ashing of the photoresist, the process conditions should be precisely controlled. Process conditions that must be so controlled include the temperature of the process chamber and the temperature of the wafer.

Known gas distribution or baffle plate assemblies for uniformly directing energized plasma onto a wafer surface generally comprise one or two parallel apertured plates that are typically made of quartz, or in the case of two parallel plates, an upper quartz plate and a lower metal plate. Quartz is generally chosen for its ability to withstand high process temperatures. However, the use of quartz makes acceptable wafer and process temperature uniformity difficult to obtain. The temperature non-uniformities may be caused by the large temperature gradients that can develop across the surface of a quartz plate due to its poor thermal conductivity characteristics. In addition, undesirable infrared (IR) wavelength absorption characteristics of quartz add to the thermal energy absorbed by the baffle plate. As a result, process uniformity and system throughput are adversely affected.

For plasma tools requiring the use of fluorine chemistries, the upper quartz plate may be further coated with a sapphire coating. The presence of the sapphire coating prevents etching of the plate from exposure to the reactive fluorine species. A solid, single plate could be fabricated entirely from sapphire; however, this is generally considered by those in the art to be cost prohibitive. The sapphire coated quartz plate may additionally include a central impingement disc formed of a ceramic material to deflect the incoming plasma jet into the process chamber plenum and also reduces the high temperature exposure to the coated sapphire material.

Several problems of these types of baffle plate assemblies are known to exist. For example, with regard to the sapphire coated plates, the sapphire coating tends to flake off after protracted use, which is believed to be due to unequal and non-conformal sidewall coating of the apertures disposed therein relative to the top and bottom surfaces of the plate. Still further, periodic replacement of the sapphire coated plate and/or ceramic disc leads to higher end costs since the sapphire coating adds significant cost to the quartz plate.

Solid ceramic baffle plates can be used to resolve many of the problems facing the prior art. However, subjecting solid ceramic plates of the size utilized in plasma process chambers to a thermal gradient during operation of the plasma can result in catastrophic failure. At a baffle plate radius greater than about 5 inches, the so-called “hoop” stresses in the plate can exceed the capability of the ceramic material causing the plate to crack. Cracking of the plate deleteriously results in particle generation as well as contaminates the process chamber, thereby requiring expensive downtime, repair, and replacement.

Accordingly, there is a need in the art for an improved baffle plate assembly that maintains plasma uniformity and can withstand the various conditions utilized during the plasma process, e.g., withstands thermal gradient related stresses, and/or is economical viable, and/or is compatible with fluorine chemistries, and/or the like.

BRIEF SUMMARY

Disclosed herein are multi-piece baffle plate assemblies, plasma processing chambers, and plasma processing systems. In one embodiment, the multi-piece baffle plate assembly comprises a generally planar multi-piece baffle plate spaced apart from and fixedly positioned above a wafer to be processed.

A plasma processing chamber for processing a semiconductor wafer contained therein, comprises a wafer processing cavity into which a wafer may be inserted for processing, the wafer processing cavity defined in part by walls including a top wall; and a baffle plate assembly located adjacent said wafer processing cavity for distributing energized gas thereinto, said baffle plate assembly comprising a generally planar upper baffle plate fixedly positioned above a generally planar lower baffle plate, said upper baffle plate comprising at least two pieces comprising at least one annular shaped ring portion having an opening and an insert portion dimensioned to sit within the opening.

A downstream plasma treatment device for treating a substrate, comprises, in combination a gas source; a plasma generating component in fluid communication with the gas source, the plasma generating component comprising a plasma tube and a plasma generator coupled to the plasma tube for generating a plasma within the plasma tube from the gas source; and a process chamber in fluid communication with the plasma tube, wherein the process chamber comprises a baffle plate assembly comprising a generally planar multi-piece baffle plate spaced apart from and fixedly positioned above the substrate to be processed.

In another embodiment, a downstream plasma treatment device for treating a substrate, comprises, in combination a gas source; a plasma generating component in fluid communication with the gas source, the plasma generating component comprising a plasma tube and a plasma generator coupled to the plasma tube for generating a plasma within the plasma tube from the gas source; and a process chamber in fluid communication with the plasma tube, wherein the process chamber comprises a baffle plate assembly comprising a generally planar upper baffle plate fixedly positioned above a generally planar lower baffle plate, said upper baffle plate comprising at least two pieces comprising at least one annular shaped ring portion having an opening and an insert portion dimensioned to sit within the opening.

A method for preventing cracking of a ceramic baffle plate having a radius greater than 4 inches during a plasma mediated process, wherein the plasma mediated process subjects the ceramic baffle plate to a thermal temperature gradient across the plate comprises forming the ceramic baffle plate into at least two pieces, wherein a gap formed by the at least two pieces is less than 0.010 inches; and exposing the least two pieces of the ceramic baffle plate to plasma formed during the plasma mediated process.

The above described and other features are exemplified by the following figures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the figures, which are exemplary embodiments and wherein like elements are numbered alike:

FIG. 1 is a sectional view of an exemplary photoresist asher into which is incorporated a first embodiment of a baffle plate assembly constructed according to the present disclosure;

FIG. 2 graphically illustrates tangential stress in a ceramic baffle plate at a given thermal gradient;

FIG. 3 is an exploded perspective view of a single layered multi-piece baffle plate assembly;

FIG. 4 is a cross sectional view of the single layered multi-piece baffle plate assembly taken along lines 4-4;

FIG. 5 is a plan view of an exemplary insert portion for a single layered multi-piece baffle plate assembly; and

FIG. 6 is a cross sectional view of the exemplary insert portion taken along lines 6-6.

DETAILED DESCRIPTION

Referring now to the drawings, FIG. 1 illustrates an exemplary photoresist asher 10, generally comprising a gas box 12, a microwave plasma generator assembly 14, a process chamber 16 defining an interior cavity in which is processed a semiconductor substrate such as a wafer 18, and a radiant heater assembly 20 for heating the wafer 18 situated at the bottom of the process chamber. A temperature probe 24, such as a thermocouple, is used to monitor the temperature of the wafer 18 during operation. A vacuum pump 26 is used to evacuate the process chamber 16 for processes requiring vacuum conditions.

An optional monochromator 28 is used to monitor the optical emission characteristics of gases within the chamber to aid in process endpoint determination. The wafer 18 is introduced into and removed from the process chamber 16 via an appropriate load lock mechanism (not shown) via entry/exit passageway 30. Alternately, the wafer 18 may be introduced directly into the process chamber 16 through the entry/exit passageway 30 if the tool is not equipped with a load lock. Although the present disclosure is shown and characterized as being implemented within a photoresist asher, it may also be used in other semiconductor manufacturing equipment, such as residue removal and strip processes. For example, downstream axial flow plasma apparatuses particularly suitable for modification in the present disclosure are plasma ashers, such as for example, those microwave plasma ashers available under the trade name RadiantStrip320 and commercially available from Axcelis Technologies Corporation. Portions of the microwave plasma asher are described in U.S. Pat. Nos. 5,498,308 and 4,341,592, and PCT International Application No. WO/97/37055, herein incorporated by reference in their entireties. As will be discussed below, the disclosure is not intended to be limited to any particular plasma asher in this or in the following embodiments. For instance, the processing plasma can be formed using a parallel-plate, capacitively coupled plasma source, an inductively coupled plasma source, and any combination thereof, with and without DC magnet systems. Alternately, the processing plasma can be formed using electron cyclotron resonance. In yet another embodiment, the processing plasma is formed from the launching of a Helicon wave. In yet another embodiment, the processing plasma is formed from a propagating surface wave.

In operation, a desired mixture of gases is introduced into a plasma tube 32 from gas box 12 through an inlet conduit 34. The plasma tube 32 can be made of alumina (Al₂O₃) or sapphire to accommodate fluorine chemistries without etching, degradation, and/or other issues associated with fluorine chemistries. The gases forming the desired mixture are stored in separate supplies (not shown) and mixed in the gas box 12 by means of valves 36 and piping 38. One example of a desired gas mixture is nitrogen-forming gas (primarily nitrogen with a small percentage of hydrogen), and oxygen. A fluorine containing gas, such as carbon tetrafluoride (CF₄), may be added to the gas mixture to increase ashing rates for certain processes.

The desired gas mixture is energized by the microwave plasma generator assembly 14 to form a reactive plasma that will ash photoresist on the wafer 18 in the process chamber 16 when heated by the radiant heater assembly 20. A magnetron 40 generates microwave energy that is coupled to a waveguide 42. Microwave energy is fed from the waveguide through apertures (not shown) in microwave enclosure 44, which surrounds the plasma tube 32.

An outer quartz cooling tube 46 surrounds the plasma tube 32, slightly separated therefrom. Pressurized air is fed into the gap between the tubes 32 and 46 to effectively cool the tube 32 during operation. The microwave enclosure 44 can be segmented into sections shown by phantom lines 45. Segmentation of the enclosure 44 can provide uniform microwave power distribution across the length of the alumna or sapphire plasma tube, and protects it from overheating by preventing an unacceptably large thermal gradient from developing along its axial length when suitable input power is provided. Each segment of the enclosures 44 is separately fed with microwave energy that passes through the quartz tube 46 and the alumna or sapphire tube 32 passing therethrough.

The gas mixture within the plasma tube 32 is energized to create a plasma. Microwave traps 48 and 50 can be provided at the ends of the microwave enclosure 44 to prevent microwave leakage. Energized plasma (typically having a temperature of about 150° C.) enters the process chamber 16 through an opening 51 in the top wall 52 thereof.

Positioned between the top wall 52 of the plasma chamber 16 and the wafer 18 being processed is a multi-piece baffle plate assembly 54. Although shown as a single layered multi-piece baffle plate assembly, it is contemplated that the multi-piece baffle plate may take the form of a dual- layered multi-piece baffle plate assembly comprising upper and lower baffle plates, wherein the upper baffle plate is formed of the multiple pieces in the manner described with respect to the single layered multi-piece baffle plate assembly. In either embodiment, the multi-piece baffle plate assemblies evenly distribute the reactive plasma across the surface of the wafer 18 being processed. Moreover, the multi-piece construction can minimize heat stresses during operation, which have been observed to cause catastrophic failure in ceramic type baffle plate assemblies having layers fabricated from a single piece of the ceramic material.

For example, as shown in FIG. 2, exposing a ceramic (alumina) baffle plate assembly to a thermal gradient across the baffle plate can result in cracking of the plate during operation as a result of hoop stresses. Ceramic materials suitable for use as baffle plates are generally stronger in compression than tension. Because of this, hoop stresses caused by thermal gradients occurring in the plate during plasma processing can exceed the material strength. In this particular example, the tensile strength of the ceramic was about 1E8 MPa to about 2E8 MPa, which is the maximum shown for about a 4 to about a 5 inch plate radius. The use of multi-piece construction as disclosed herein, permits the use of materials such as ceramics for fabrication of the baffle plate(s) without causing premature cracking by preventing the hoop stresses from exceeding the material strength. As such, ceramic multi-piece baffle plate assemblies provide an inexpensive alternative to sapphire coated baffle plate assemblies and eliminate the problems associated with the use of sapphire coatings. The multi-piece ceramic baffle plate is especially desirable for processes including fluorine chemistries.

With reference back to FIG. 1, in operation, the reactive plasma passes through the multi-piece baffle plate 54 and can be used to ash the photoresist and/or residues on the wafer 18. The radiant heater assembly 20 comprises a plurality of tungsten halogen lamps 58 residing in a reflector 56 that reflects and redirects the heat generated by the lamps toward the backside of the wafer 18 positioned within the process chamber 16 on quartz or ceramic pins 68. One or more temperature sensors 72, such as thermocouples, can be mounted on the interior of process chamber sidewall 53 to provide an indication of wall temperature.

The single layered multi-piece baffle plate assembly 54 comprises a generally planar gas distribution central portion 74, having apertures 76 therein, surrounded by a flange 78. The flange 78 surrounds the central portion and seats intermediate the process chamber sidewall 53 and top wall 52. Seals 79 and 81, respectively, provide airtight connections between the flange 78 and the sidewall 53, and between the flange 78 and the top wall 52. The seals 79 and 81 reside in grooves located in the flange 78. The flange 78 also provides mounting holes (not shown) for mounting to the top wall 52 and sidewall 53.

As shown more clearly in FIGS. 3-6, the illustrated single layered multi-piece baffle plate assembly 54 comprises a two-piece construction. However, although the figures illustrate a two-piece construction, greater than two pieces are contemplated and may actually be desired for certain applications. Moreover, it should be apparent to those skilled in the art that the shapes of the various pieces to form the baffle plate are not intended to be limited to any particular shape or aperture pattern. It has been found that the use of multiple pieces to form the baffle plate advantageously relieves the thermal stresses introduced during plasma operation, the design of which is virtually limitless as will be appreciated by those skilled in the art in view of this disclosure.

In FIG. 3, there is illustrated an exploded perspective view of the multi-piece baffle plate assembly 54. The multi-piece baffle plate assembly 54 generally comprises a generally annular shaped ring 90 and an insert portion 92 centrally located within an opening 94 defined by the generally annular shaped ring 90. As illustrated, the exemplary single layered multi-piece baffle plate 54 comprises a hexagonally shaped opening 94 and a hexagonally shaped insert portion 92. In this embodiment, the hexagonal shape was chosen to accommodate a desired flow pattern for a particular plasma ashing application. As previously described, the annular ring as well as the number of pieces forming the single layered baffle plate assembly can define any opening shape. Again, although applicant refers to an annular ring, it is contemplated that the various pieces do not include an annular ring. Rather, the multiple pieces are configured and constructed so as to form a single layer of the baffle plate. A locking means would be included to maintain the baffle plate in a generally planar configuration and is well within the skill of those in the art.

FIG. 4 illustrates a cross sectional view of the single layered multi-piece baffle plate assembly 54. The opening 94 of the annular shaped ring 90 includes a recessed portion 96 dimensioned to receive a shoulder portion 98 formed about an outer edge of the inert portion 92 (shown more clearly in FIG. 6). Optionally, three or more support pins 100 are radially disposed in the shoulder 98 at equidistant positions about the annular recessed portion to minimize scraping (and possible particle generation) between the insert portion and the annular shaped ring. A gap formed between the insert portion 92 and the annular shaped ring 90 is less than about 0.010 inches to allow radial expansion during plasma operation and provide a net surface that is wetted by the plasma as if the baffle plate were formed a single unitary piece. FIGS. 5 and 6 depict the insert portion 92. As shown, the insert portion 92 includes a non-apertured central portion.

The so-formed single layered multi-piece baffle plate generally includes a plurality of apertures, wherein the apertures are arranged in a radial (or concentric multiply circular) pattern. The single layered multi-piece baffle plate may or may not include a non-apertured central portion as may be desired for certain plasma applications. The design of the baffle plate assembly (single or dual layered) is generally determined by applied gas dynamics, materials engineering, and process data to insure correct pressure, gas flows, and temperature gradients within the process chamber.

In the case of a dual layered multi-piece baffle plate assembly, the upper baffle plate and/or the lower baffle plate can be comprised of multiple pieces in the manner previously described. For example, the upper baffle plate can be formed of multiple pieces, wherein the lower baffle plate is formed of a single unitary piece. In the dual layered configuration, the apertures in the upper baffle plate are slightly larger than the apertures in the lower baffle plate. Moreover, it may be preferred to have a central non-apertured portion within the upper baffle plate. In this manner, the non-apertured portion diverts the energized gases from the plasma tube radially outward to the remaining apertured area of the upper baffle plate so as to prevent the radially inward portion of the wafer being preferentially processed before the outward portion of the wafer. The distance between the upper and lower baffle plates, in part, determines the pattern of gas flow through the dual layered baffle plate assembly. Apertures are provided in the radially inner portion of the lower baffle plate but generally not in the radial external portion. The surface area of the radially inner portion of the lower baffle plate is sufficient to cover the wafer residing therein below. In one embodiment, the apertures are generally positioned equidistant from each other in all directions. That is, any three apertures that are mutually immediately adjacent to each other form an equilateral triangle. Other distributions of holes on the baffle plates may also be of used for specific applications such as, for example, larger holes on the outer diameters but smaller holes on the inside diameters so as to improve ash uniformity. Moreover, it is noted that the dual layered baffle plate assembly is generally compact, requiring less than one-inch vertical space within the process chamber.

The upper multi-piece baffle plate is preferably formed from a ceramic material. Suitable ceramic materials include, but are note intended to be limited to, alumina (various aluminum oxides), zirconium dioxides, various carbides such as silicon carbide, boron carbide, various nitrides such as silicon nitride, aluminum nitride, boron nitride, quartz, silicon dioxides, various oxynitrides such as silicon oxynitride, and the like as well as stabilized ceramics with elements such as magnesium, yttrium, praseodymia, haffiium, and the like. Optionally, the lower single piece baffle plate can be the same or of a different material, typically anodized aluminum.

The disclosure is further illustrated by the following non-limiting examples.

EXAMPLES

In the following examples, a plasma asher was configured with a dual layered multi-piece baffle plate assembly and separately with a conventional dual layered baffle plate assembly. Typical data were acquired and analyzed, comparing the two configurations. The upper baffle plate of the dual layered multi-piece baffle plate assembly was of a two-piece construction similar to that shown in FIGS. 3-6 and formed from high purity alumina. The baffle plate assemblies for the two configurations were identical with the exception of the multi-piece construction of the upper baffle plate in the dual layered multi-piece baffle plate assembly. The baffle plate assemblies were subjected to a low temperature plasma ashing process (120° C.) and a high temperature plasma ashing process (270° C.). Gas flow, pressure and microwave power were identical. The results are shown in Tables 1 and 2, respectively. Ashing rate and plasma uniformity were compared for the two baffle plate assemblies. TABLE 1 Standard Baffle Plate Ash Rate Deviation % Non- Standard Type (μm/min) (μm/min) uniformity (1σ) Deviation (1σ) Control 0.13 0.002 8.71 0.012 Multi-piece 0.12 0.001 11.14 0.209 Ceramic

TABLE 2 Standard Baffle Plate Ash Rate Deviation % Non- Standard Type (μm/min) (μm/min) uniformity (1σ) Deviation (1σ) Control 7.75 0.10 4.1 0.26 Multi-piece 7.27 0.02 4.75 0.16 Ceramic

The results indicate that the use of the multi-piece construction provided similar ashing behavior.

In this example, the generation of particle adders greater than 0.12 nanometers that were deposited onto the wafer during plasma ashing was monitored. The results are shown in Table 3. TABLE 3 Ash Rate Standard Baffle Plate Type (μm/min) Deviation (1σ) Control 53 16.82 Multi-piece Ceramic 87 10.02

The results show that the use of the ceramic multi-piece did not contribute significantly to particle adder generation.

In this example, time to end point was monitored for a plasma ashing process. Photoresist was coated onto 300 millimeter wafers at a thickness of 1.0 micron. The results are shown in Table 4. TABLE 4 Time to Standard Baffle Plate Endpoint (Seconds) Deviation Control 10.43 0.41633 Multi-piece Ceramic 11.80 0.1000

The results show that the time for ashing the photoresist was not significantly different for the plasma asher configured with the multi-piece ceramic baffle plate assembly as described.

While the disclosure has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims. 

1. A baffle plate assembly for distributing plasma into an adjacent process chamber containing a semiconductor wafer to be processed, comprising: a generally planar multi-piece baffle plate spaced apart from and fixedly positioned above a wafer to be processed.
 2. The baffle plate assembly of claim 1, wherein the generally planar multi-piece baffle plate comprises at least one annular shaped ring portion having an opening and an insert portion dimensioned to sit within the opening.
 3. The baffle plate assembly of claim 2, wherein the opening comprises an annular recessed portion and the insert portion comprises a lip adapted to seat on the annular recessed portion.
 4. The baffle plate assembly of claim 3, wherein the annular recessed portion further comprises at least three pins spaced equidistantly about the annular recessed portion, wherein the insert portion is supported by the at least three pins.
 5. The baffle plate assembly of claim 1, wherein the multi-piece baffle plate comprises a non-apertured central portion.
 6. The baffle plate assembly of claim 1, wherein the baffle plate assembly comprises an upper baffle plate and a lower baffle plate, wherein the upper baffle plate comprises the multi-piece baffle plate, wherein the multi-piece baffle plate has a non-apertured central portion.
 7. The baffle plate assembly of claim 2, wherein the annular shaped ring and the insert portion form a gap less than 0.010 inches.
 8. The baffle plate assembly of claim 1, wherein the multi-piece baffle plate is formed of a ceramic material.
 9. A plasma processing chamber for processing a semiconductor wafer contained therein, comprising: a wafer processing cavity into which a wafer may be inserted for processing, the wafer processing cavity defined in part by walls including a top wall; and a baffle plate assembly located adjacent said wafer processing cavity for distributing energized gas thereinto, said baffle plate assembly comprising a generally planar upper baffle plate fixedly positioned above a generally planar lower baffle plate, said upper baffle plate comprising at least two pieces comprising at least one annular shaped ring portion having an opening and an insert portion dimensioned to sit within the opening.
 10. The plasma processing chamber of claim 9, wherein said upper baffle plate is comprised of a ceramic material.
 11. The plasma processing chamber of claim 9, wherein the opening comprises an annular recessed portion and the insert portion comprises a lip adapted to seat on the annular recessed portion.
 12. The plasma processing chamber of claim 11, wherein the annular recessed portion further comprises at least three pins spaced equidistantly about the annular recessed portion, wherein the insert portion is supported by the at least three pins.
 13. The plasma processing chamber of claim 9, wherein the upper baffle plate comprises a non-apertured central portion.
 14. The plasma processing chamber of claim 9, wherein the annular shaped ring and the insert portion form a gap less than 0.010 inches.
 15. The plasma processing chamber of claim 9, wherein the chamber is adapted to receive a wafer having a diameter of at least 200 millimeters.
 16. A downstream plasma treatment device for treating a substrate, comprising, in combination: a gas source; a plasma generating component in fluid communication with the gas source, the plasma generating component comprising a plasma tube and a plasma generator coupled to the plasma tube for generating a plasma within the plasma tube from the gas source; and a process chamber in fluid communication with the plasma tube, wherein the process chamber comprises a baffle plate assembly comprising a generally planar multi-piece baffle plate spaced apart from and fixedly positioned above the substrate to be processed.
 17. The downstream plasma treatment device of claim 16, wherein the multi-piece baffle plate is formed of a ceramic material.
 18. The downstream plasma treatment device of claim 16, wherein the generally planar multi-piece baffle plate comprises at least one annular shaped ring portion having an opening and an insert portion dimensioned to sit within the opening.
 19. The downstream plasma treatment device of claim 18, wherein the opening comprises an annular recessed portion and the insert portion comprises a lip adapted to seat on the annular recessed portion.
 20. The downstream plasma treatment device of claim 19, wherein the annular recessed portion further comprises at least three pins spaced equidistantly about the annular recessed portion, wherein the insert portion is supported by the at least three pins.
 21. The downstream plasma treatment device of claim 16, wherein the multi-piece baffle plate comprises a non-apertured central portion.
 22. The downstream plasma treatment device of claim 18, wherein the annular shaped ring and the insert portion form a gap less than 0.010 inches.
 23. A downstream plasma treatment device for treating a substrate, comprising, in combination: a gas source; a plasma generating component in fluid communication with the gas source, the plasma generating component comprising a plasma tube and a plasma generator coupled to the plasma tube for generating a plasma within the plasma tube from the gas source; and a process chamber in fluid communication with the plasma tube, wherein the process chamber comprises a baffle plate assembly comprising a generally planar upper baffle plate fixedly positioned above a generally planar lower baffle plate, said upper baffle plate comprising at least two pieces comprising at least one annular shaped ring portion having an opening and an insert portion dimensioned to sit within the opening.
 24. The downstream plasma treatment device of claim 23, wherein the upper baffle plate is formed of a ceramic material.
 25. The downstream plasma treatment device of claim 23, wherein the upper baffle plate comprises at least one annular shaped ring portion having an opening and an insert portion dimensioned to sit within the opening.
 26. The downstream plasma treatment device of claim 25, wherein the opening comprises an annular recessed portion and the insert portion comprises a lip adapted to seat on the annular recessed portion.
 27. The downstream plasma treatment device of claim 26, wherein the annular recessed portion further comprises at least three pins spaced equidistantly about the annular recessed portion, wherein the insert portion is supported by the at least three pins.
 28. The downstream plasma treatment device of claim 23, wherein the upper baffle plate comprises a non-apertured central portion.
 29. The downstream plasma treatment device of claim 25, wherein the annular shaped ring and the insert portion form a gap less than 0.010 inches.
 30. A method for preventing cracking of a ceramic baffle plate having a radius greater than 4 inches during a plasma mediated process, wherein the plasma mediated process subjects the ceramic baffle plate to a thermal temperature gradient across the plate, the method comprising: forming the ceramic baffle plate into at least two pieces, wherein a gap formed by the at least two pieces is less than 0.010 inches; and exposing the least two pieces of the ceramic baffle plate to plasma formed during the plasma mediated process.
 31. The method of claim 30, wherein the at least two pieces comprises at least one annular shaped ring portion having an opening and an insert portion dimensioned to sit within the opening.
 32. The method of claim 30, wherein exposing the at least two pieces of the ceramic baffle plate to plasma subjects the at least two pieces to hoop stresses less than a material stress for the ceramic. 